Climate change: Satellites record history of Antarctic melting

Twenty-five years of satellite observations have been used to reconstruct a detailed history of Antarctic ice sheets.

These ice platforms are the driving protrusions of glaciers flowing out of the land, encircling the entire continent.

The European Space Agency’s dataset confirms the melting trend of the planks.

As a whole, they have been dumping close to 4,000 gigatons since 1994 – an amount of meltwater that could fill anything but America’s Grand Canyon.

But the innovation here is not so much the fact that the planks are losing mass – we already knew that; relatively warm ocean water eats its undersides. After all, these are the finesse statements that can now be made about exactly where and when the devastation took place, and where the meltwater also went.

Some of this cold, fresh water has entered the deep sea around Antarctica, where it undoubtedly affects the circulation of the ocean. And this may have implications for the climate far beyond the polar south.

“For example, there have been a few studies that have shown that including the effect of Antarctic ice melting in models slows the rise in ocean temperature, and that may actually lead to an increase in precipitation in the US,” he explained. Susheel Adusumilli of the Scripps Institution of Oceanography in San Diego.

Mr. Adusumilli and colleagues analyzed all observations made by Esa’s long series of radar altitude missions – ERS-1, ERS-2, EnviSat and CryoSat-2.

These spacecraft have detected the change in thickness of Antarctic ice sheets since the early 1990s.

Combining their data with ice velocity information from other sources, and the output of computer models – the Scripps group has obtained a high-resolution view of the pattern of melts during the study period.

As one would expect, there was quite a lot of variation, with mass loss and gain, even within the same individual shelf. And the rate of mass loss over time has also gone up and down. But the general picture is clear: the planks are crumbling.

“We see that melts are always above stable state values,” Mr Adusumilli told BBC News. “You need some melting to keep the ice sheet in balance. But what we’ve seen is some melting through the ocean that is more than necessary to keep it in balance.”

The fascinating aspect to this study is that scientists can now also detect exactly where at depth the melting occurs. Some of these floating ice platforms (the largest being the size of France) extend many hundreds of meters below sea level.

The researchers can tell from the satellite data whether the erosion occurs near the thin parts of the planks or at their fronts, or deep down in those places where the glacier that comes from the land first becomes drifting and begins to drift.

“That kind of information can tell us a lot about the melting processes involved, how they work – and the effects that meltwater can have,” said Prof Helen Fricker of Scripps.

“That, it’s not just that the planks are melting. It’s how they melt – and where their meltwater is pumped into the ocean.”

Thin ice sheets do not directly contribute to sea level rise. This is because the floating ice has already displaced its equivalent volume of water.

But there is an indirect consequence. If the planks are weakened, the land ice behind can flow faster into the ocean, and this will lead to rising sea levels. This happens, and is measured by other satellites.

Prof David Vaughan is the Director of Science at the British Antarctic Survey. He was not associated with the study published in Nature Geoscience.

He told BBC News: “The Scripps team has produced a map of Antarctica that shows thinning around the margin in a strip of bright red and blue colors. The detail along the coastline is absolutely phenomenal.

“We can now really identify the parts of ice planes that are most crucial to the story of thinning. Many oceanographers will spend a lot of time looking at where melting and thinning actually occur, and try to work out exactly why these areas have been affected. ”

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